Flash lamp



Sept. 19, 1961 w. F. ALBRECHT FLASH LAMP Filed June 3, 1958 lnvah tor'. Warven F ALbT'ecW-"L', b8 W 31%- His A t tovnes United States Patent 3,000,200 FLASH LAMP Warren F. Albrecht, Euclid, Ohio, assignor to General Electric Company, a corporation of New York Filed June 3, 1958, Ser. No. 739,579 2 Claims. (Cl. 6731) This invention relates to flash lamps of the type comprising a semed glass bulb and combustible material within the bulb to produce, when ignited, a flash of light suitable for photographic purposes.

Photographic flash lamps in commercial use at present generally provide bulbs of pear-shape, ellipsoidal shape, or similar single ended shapes, fitted with a base of screw, bayonet, or other type containing electrical contacts.

An object of the present invention is to provide a flash lamp bulb having an improved physical shape and apearance and possessing numerous desirable features and characteristics over that inherent in the prior bulbs. Further objects and advantages of the invention will appear from the following detailed description of a species thereof and from the appended claims.

Briefly stated, a flash lamp according to the present invention comprises a sealed glass cylindrical bulb containing a charge of combustible material and ignition means sealed therein. The electrical contacts forthe ignition means are recessed into the ends of the bulb and hermetically sealed therein.

Some designs of flash lamps permit the lamp to be flashed on high voltage, low energy power; such energy may be well below the amount which can be accumulated electrostatically on various objects. The static energy accumulation must therefore be kept away from the lamps electrical contacts and ignition means. Recessing the contacts a sufflcient distance to prevent accidental contact between the contacts in the ends of the lamp and statially charged objects effectively isolates the lamps ignition means from electrostatic charges, yet permits easy access by suitable cooperating contacts when assembled in a flash gun.

The recessed contacts afford the further advantage of being out of corrosive contact with the human hands. The bulb has the further advantage of being a convenient non-locating bulb, so that the bulb may be placed in the socket in only the correct manner without necessity of alignment of parts. By the elimination of external base, the lamp contains a large inside to outside volume ratio permitting a smaller sized bulb for a given light output and safety factor, thus being more convenient for carrying by the photographer. Further, because the bulb walls are inherently heavy, the lamp is safer at higher bulb pressures; this means that less protective enclosing lacquer can be applied to the bulb wall. Further, such a bulb as herein disclosed permits the bulb to be conveniently loaded in magazines for rapid changing of the lamps in the flash gun.

Certain manufacturing advantages are inherent in this design. The design therefore results in a cheaper and easier design than conventional methods. Further, because the primer for the ignition means may be inserted after sealing of the contacts and lamp, the primer is not subjected to destructive effects of sealing heat.

Referring to the accompanying drawings, an embodiment of the invention is shown in which:

FIG. 1 is a sectional view of a flash lamp embodying the invention, and

FIG. 2 is a sectional view of a formed glass blank which may be used in making the finished lamp bulb.

Referring to FIG. 1, the flash lamp according to the present invention comprises a hermetically sealed vitreous envelope or bulb 1 of substantially cylindrical shape,

3,000,200 Patented Sept. 19, 1961 closed at the ends. Sealed within the bulb is a charge of readily combustible material 2, herein disclosed as shredded metallic foil, which may be aluminum, magnesium, zirconium, and the like, and mixtures and alloys thereof; however, the combustible material may constitute wire, crumpled foil, beads or coatings of readily ignitable light producing material. The bulb contains a charge of combustion supporting gas. Ignition means are contained within the lamp for initiating the combustion of the readily combustible material. The ignition means may consist of the type including a fine tungsten filament which may be heated to incandescence and which type is presently available on commercial flash lamps; or the ignition means may consist of one of the filamentless type photoflash lamps heretofore proposed, for example, the lamp described and claimed in co-pending application Serial No. 639,959, new Patent No. 2,868,003, filed February 13, 1957 by Albrecht, and assigned to the assignee of the present invention. As shown, for purposes of initiating the combustion, the lamp is provided with a pair of internal electrodes 3, 4, electrode 4 being provided with a primer composition 5, arranged so that the combustible material 2 provides a conducting path between the electrodes whereby a power surge will form small arcs between electrode 4 and the combustible material 2 through the primer 5 and thus ignite the primer and, through it, initiate combustion of the combustible material. The electrodes 3, 4 are secured to electrical contracts 6, 7 hermetically sealed in the ends of the bulb and recessed into said ends.

The primer composition 5 may be of the same composition as that employed generally in the conventional filament type flash lamps. Such primer generally comprises a porous mixture of a readily ignitable metallic powder such as zirconium or a mixture of zirconium with magnesium, and an oxidizing agent such as potassium perchlorate, bonded together by a suitable binder such as nitrocellulose. By way of example, a suitable primer composition may consist of, by Weight, zirconium and 10% potassium perchlorate formed as a suspension in a solution of nitrocellulose in amyl acetate and having a viscosity of about 24 centipoisesx grams per cubic cm.

The body portion of the bulb 1 is of approximately cylindrical shape having a diameter D and length A. However, the corners of the cylinder may be slightly rounded, as shown by r so as to make the lamp bulb with a smooth curvature thereby rendering the bulb easier to manufacture, making it more pleasing in appearance, easier to handle, and otherwise improving the bulb. Such a rounding may be made with a radius r so that the body portion of the bulb which encloses the combustible material contains a center zone of approximately cylindrical shape, distance B; the end zones, distance C, due to the rounding of the edges by radius r have approximately the shape of a toroid generated by revolving a surface of approximately semicircular crosssection with a radius approximately equal to r about an axis coincident with the longitudinal axis of the bulb, E-E. The outer perimeter of the toroid tangentially intersects the surface of the cylindrical center zone so as to form a smooth curvature in the cross-sectional periphery. In order to produce a recessed center portion in the bulb -1 in which the end contacts 6, 7 are sealed, the radius of the semicircle of revolution, r forming the toroid must be less than one-half the radius r of the cylindrical center portion.

Electrical contacts 6, 7 are hermetically sealed into one or both ends of the lamp bulb as needed.

By way of example, but not limitation, the flash lamp bulb may be made from a glass blank shown in FIG. 2. The glass blank therein illustrated can be formed from A 3 a section of glass tubing. Because of the inherent thickness t of the wall of the glass tubing, the heavy bulb walls produce a safer lamp at higher bulb pressures. During manufacture, the ends of the glass blank 8, 9 are preheated. The contacts 6, 7 which may be of the type illustrated in FIG. 1, are then butted against the openings 10, 11 in the glass blank; The glass and the contacts are then further heated, if necessary; this is advantageous inasmuch as the heating creates an oxide on the contacts 6, 7 which permits better sealing with the glass. The contacts 6, 7 are then plunged intothe bulb a preset distance and held momentarily until the glass fuses. 'Ihe contacts 6, 7 may be of a cup-shape, as illustrated in FIG. 1. One contact 7, may contain an electrode '4 secured thereto; while the other contact 6, may be of an open cup-shape or eyelet-shape that does not yet have its associated electrode 3 assembled therewith and, when assembled with the blass bulb, has an opening 12, FIG. 1. The primer 5 may then be introduced through the opening 12, the bulb may be filled with shredded foil and the bulb exhausted and filled with a combustion supporting gas such as oxygen. Electrode 3 may then be assembled with the contact 6 and heremetically sealed thereto, as for example, by solder 13.

In actual bulbs formed in accordance with the invention, the over-all length A of the body portion approximates a cylinder and was .768 inch; the length of the cylindricalcenter zone B was .467 inch; the projected length of the toroid of revolution C was .158 inch; the diameter D was .695 inch. The typical radius T of the toroid of revolution was in the range of about .125 to about .158 inch. The radius r of the cylindrical portion is, of course, one-half the diameter D. The glass has a typical wall thickness t of about .040 inch. All dimensions given for radii and diameter are outside dimensions.

The electrical contacts 6, 7 are recessed a suflicient distance that they are free of contact from statically charged objects. However, they are conveniently located for contact with cooperating socket contacts (not shown) mating with contacts 6, 7. While the contacts 6, 7 may be of any desired shape the particular contacts illustrated are cup-shaped, having an internal diameter of approximately .125 inch; the upper portion of the cups as shown are recessed, distance F, .086 inch; the lower portion of the cups as shown are recessed, distance G, .158 inch. The inside volume of these bulbs is 2.77 cc. The ratio of the diameter D ofthe body portion of the bulb to the over-all length A thereof was approximately .905.

As stated above, the toroid forming the end zones C has the approximate cross-section of a semicircle; but may vary from a semicircle due to the manufacturing tolerances and methods of manufacturing. Further, while the wall thickness t of the bulb is relatively heavy, the wall thickness of the bulb may vary due to the meth- 4 ods of manufacturing, particularly in the area of the minor diameter of the toroid in which the electrical contacts 6, 7 are sealed. Such a thickened section of glass at this particular bulb location is advantageous in reinforcing the bulb at one of its heaw'er stressed points.

Many modifications may occur to one skilled in the art, for example, the bulb herein disclosed may be used with a single electrode type flash lamp; thereby requiring only one electrical contact. The invention is to be limited only by the claims annexed to and forming a part of this specification.

- What I claim as new and desire to secure by Letters Patent of the United States is:

1. A flash lamp comprising a sealed glass bulb containing a charge of combustible flash material and electrostatically dischargeable ignition means for initiating combustion of said charge, a pair of electrical contacts on said bulb hermetically sealed in said bulb and means for preventing accidental electrostatic discharge of said combustible flash material including recesses in said bulb in which said contacts are placed.

2. A flash lamp comprising a charge of combustible flash material, electrostatically dischargeable ignition means for initiating combustion of said charge, a pair ofelectrical contacts for discharging said ignition means and hence said combustible charge, and means for preventing accidental electrostatic discharge of said ignition means including a sealed glass bulb enclosing said charge and said ignition means, said bulb being shaped to include a body portion having a center surface and two end surfaces of diiferent contour from the center surface, said center surface being approximately cylindrical in shape, the end surfaces having approximately the shape of a toroid generated by revolving a generatrix of approximately semi-circular cross-section about an axis coincident with the longitudinal axis of the bulb, the radius of the semi-circular cross-section being less than the radi us of the cylindrical center surface, the outer perimeter of the toroid tangentially intersecting the center surface so as to form a smooth curvature with said center surface of the body portion, the electrical contacts being placed in recesses in the center of the respective toroidalshaped ends of the bulb to conceal them.

References Cited in the file of this patent UNITED STATES PATENTS 

